Legislation is due to be introduced in Mexico City on Tuesday that will legally recognise 'gay unions'.

The proposal, which has caused a huge stir in this conservative Catholic nation, comes from the left wing Democratic Revolution Party, which has control over Mexico City's government.

If it is passed the legislation would allow what is known as 'civil solidarity' for gay couples who have been living together for more than two years.

Equal rights

The law would not formally allow gay marriages, although it would extend the same legal rights as heterosexual couples living in a de facto relationship.

Cardinal Rivero has called it an attack on the family

The Democratic Revolution's leader in the legislature, Amando Kintero, said the move was aimed at advancing the human and civil rights of homosexuals who are considered free and equal under the constitution.

But outside the capital, Mexican culture is deeply Catholic and traditionally scornful of gays, and the proposal has already drawn scathing criticism.

Cardinal Noberto Rivero described it as an attack on the family.

No guarantee of success

There is no guarantee that the bill will pass through the legislature.

The Democratic Revolution is the largest party there, but it is a long way from holding an absolute majority of seats.

The other two parties in the state government are both more conservative and many of their members will fight the move.